Process for the manufacture of chromium ore containing bricks



Patented May 4, 1937 PROCESs FOR THE MANUFACTURE CHROMIUM ORE CONTAINING BRICKS Fritz Hartmann, Dortmund-Horde, Germany, assignor, by mesne assignments, to Magnesital Gesellschaft mit beschrankter Haftung, Koln- Mulheim, Germany No Drawing. Continuation of application Serial No. 484,940, September 2'7, 1930. This application June 21, 1934, Serial No. Germany September 2'1, 1929 I (01. 25-156) The invention relates to a process for the man- 15 Claims ufacture of chromium ore containing bricks and to the improved bricks thus obtained. This application is a continuation of application 484,940 5 filed September 27, 1930.

The chromium ore bricks hitherto known possess, it is true, a great resistance against the attack of acid and basic slags, but they can be utilized only in such furnaces, in which did not occur too high temperatures, since they softened under the pressure of the bricks or of their own weight, if they were subjected to high temperatures. Thus the hitherto known chromium-ore bricks collapsed if applied. in open hearth furnaces under the attack of the high temperatures prevailing therein, thus making impossible their utilization in such furnaces. Upon testing such bricks in the laboratory in accordance with the prescriptions of the German industrial norm Din 104 for the determination of the fire resistance under pressure they softened under a load of 1 kg./cm.= at 1400 to 1490 C. and they wholly collapsed at 1550 to 1640 C. In furnaces in which such temperatures may occur or are even the rule their utilization was therefore impracticable.

Now the present invention relates to a process for the manufacture of a chromium-ore containing brick which possesses a fire resistance under pressure which was hitherto unattainable. The beginning of itssoftening under load (determined according to Din 1064) lies substantially higher than that of the hitherto known chromium-ore bricks and as high as that of sillea-bricks. For this reason the bricks manufactured in accordance with my invention could be successfully used even as interior supports in ,open hearth furnaces. s- Here-they are even superior to silicaand magnesite-bricks.

40 The process of producing the new chromiumore bricks is carried out b'y'mixing 20-90% of a chromium-ore containing more than 30% of chromium oxide with 80-10% of highly sintered or molten magnesium oxide containing substances originating from magnesite or from magnesium compounds obtained in chemical processes, forming bricks therefrom and burning them. It is also possible to use therein as magnesium oxide containing substances masses obtained by highly sinteringor meltingoi'dolomite.

In a formerly known processmagnesite bricks have been manufactured from sintered magnesite or dolomite with an addition of a small amount of chromium ore as binder. Such bricks, however, do not possess the high resistance 55 against slags of all kinds as chromium-ore bricks,

but they are only resistant against basic slags and unstable against acid slags. They also fail to have a suflicient fire-resistance under pres sure.

From said prior process the new process is 5 distinguished by using mixtures containing besides highly sintered magnesium oxide com-. pounds at least 20% and not more than 90% of chromium ore. ,The particular proportions chosen within said limits depend upon the com- 10 position of the initial materials and of the quantity of other constituents incorporated into the mixture by theJchromium-ore and the magnesite, magnesia compound, dolomite or the like. The composition is furthermore to be adapted to the 15 available devices and furnaces.

Whereas it has also been proposed to manufacture a fire resistant brick from a mixture of molten magnesium spinell chromium-ore and usual inorganic and organic binding means, 90 wherein the magnesia spinell has been obtained from magnesia containing substances and further substances containing the trivalent oxidesin a difficult process, the mixture used in accordance with the present invention contains the highly sintered or molten magnesia containing substances principally in the form of magnesia and only small amounts of trivalent oxides are permissible therein.

As has been said, it is anessential condition for obtaining the desired fire resistance under load, that the magnesia containing substances are incorporated into the mixture after they have been subjected to a thermal treatment in which they are highly sintered or molten. By this term a sintering treatment is to be understood which has-been carried outat a temperature lying remarkably higher than that temperature which would be suflicient. for causing the beginning of a sintering. It has been found 40 that by using caustic or only dead/burnt magnesia compounds a substantially lower fire resistance is obtained than by highly sintered magnesia. In order to clearly distinguish my 1nvention from processes in which lowly sintered materials have been used in the ensuing claims it is said that the sintering is to be carried out at a relatively hightemperature of at least 1600 C. At such a high degree of sintering in normal magnesia containing substances a remarkable increase of the size,of the crystals is to be observed in the Roentgen diagram showing a size of crystals of at least 0.1' to 0.01 mm in the periclase lines. Such a degree of sintering is in ordinary materials i. e. in usual magnesia containing materials secured if the sintering is effected at a temperature above 1600 0. However, the required temperature depends to a certain degree from the degree of purity of the used raw materials. If, for instance exceedingly 5 pure magnesites are used it may be necessary to go still above the temperature of 1600 C. so that the temperature may vary between for instance 1600 and 2000 C. As upper limit the temperature at which the substance melts is to be regarded. w

In the process of the invention it is also possible to make use of molten magnesia or molten substances containing magnesia.

In carrying out the new process bricks of high value are obtained if the substances containing the magnesium oxide which are to be mixed with the comminuted chromium ore, are used in a finely ground condition. The chromium ore has, however, preferably a somewhat larger. grain.

The mixture can also be obtained by first producing an intimate and fine grained mixture of a part of the chromium-ore and of the magnesium-oxide containing materials and thereupon adding the remaining part of the constituents in a coarser form for the purpose of reducing the unctuosity.

For instance satisfactory results were obtained in making the finer constituents smaller than mm. whereas the coarserparts had a grain of a size of more than 2 mm. Since the chromium ore as well as the magnesium oxide containing materials possess a relatively low binding power, prior to the treatment for reducing the unctuosity, especially in the case of bricks of larger dimensions, which cannot be hydraulically pressed, small amounts of compounds of alkali metals, of metals of the alkaline earths or of other metals and if suitable also organic binders,

such as cellulose pitch lye, tar, oil, dextrine and the like, may be added to the mixture. Such additions come also into question if the mixture is obtained in a single mixing operation. Furthermore it is of advantage to use high pressures of at least 150 kg./cm. for instance.

The pressed pieces thus obtained are dried in usual manner and burnt in a similar manner as silica stones, preferably with an oxidizing flame. By enhancing the burning degree by increasing the duration and temperature of burning the favourable qualities of the bricks are further improved.

-By maintaining the above described conditions it has been possible to manufacture bricks which under a load 1 kg./cm. and the testing conditions prescribed in the German norm Din 1064 showed an incipient softening at 1680 C. and a collapse at 1720 C.

What I claim and-desire to secure by Letters Patent of the United States is:

nesium oxide containing material at a temperature of at least 1600 C., mixing the sintered portion as to cause the resulting mixture to con- 1. The process for manufacturing highly refractory bricks, which consists in sintering magtain from to 10 parts of magnesium oxide and from 20 to 90 parts of chromium'ore, containing at least 30% of chromium oxide, pressing said mixture thus obtained, and drying and burning the mixture into bricksof the desired shape. 5

3. The process for manufacturing highly refractory bricks, which consists in sintering magnesium oxide containing material at a temperature of at least 1600 C., mixing the sintered material together with chromium ore in such proportions as to cause the resulting mixture to contain from 80 to 10 parts of magnesium oxide and from 20 to 90 parts of chromium ore, containing at least 30% of chromium oxide, pressing said mixture thus obtained at a high pressure and drying and burning the mixture into bricks of the desired shape.

4. The process for manufacturing highly refractory bricks, which consists in sintering magnesium oxide containing material at a temperature of at least 1600 C., mixing the sintered material together with chromium ore in such proportions as to cause the resulting mixture to contain from 80 to 10 parts of magnesium oxide and from 20 to 90 parts of chromium ore, containing at least 30% of chromium oxide, pressing said mixture thus obtained and drying and burning the mixture under oxidizing conditions into bricks of the desired shape.

5. The process for manufacturing highly refractory bricks, which consists in sintering magnesium oxide containing material at a temperature of at least 1600 C., mixing the sintered ma terial in the presence of binding material together with chromium ore in such proportions as to cause the resulting mixture to contain from 80 to 10 parts of magnesium oxide and from 20 to 90 parts of chromium ore containing at least 30% of chromium oxide, pressing said mixture thus obtained and drying and burning the mixture into bricks of the desired shape.

6. The process for manufacturing highly refractory bricks, which consists in sintering magnesium oxide containing material at a temperature of at least 1600 C., mixing the sintered material together with chromium are in two stages, the constituents mixed together in the first stage being of finer grain andrthose mixed in the second stage being relatively coarser and said constituents being mixed in such proportions as to cause the resulting mixture to contain from 80 to 10 parts of magnesium oxide and irom 20 to 90 parts ofchromium ore, pressing said mixture thus obtained and drying and burning the mixture into bricks of the desired shape.

7. The process for manufacturing, highly refractory bricks, which consists in sintering magnesium oxide containing material at a temperature of at least 1600 C., mixing the sintered material together with chromium ore in two stages, the constituents mixed together in the first stage being of finer grain and those mixed in the second stage being:relativelycoarser and said constitu ents being mixed in such proportions as to cause the resulting mixture to. contain f-rom 80 to 10 parts of magnesium oxide and from 20 to parts of chromium ore containing at least 30% of chromium oxide, pressing said mixture thus obtained and drying and burning the mixture into bricks of the desired shape.

8. Improved refractory bricks which are stable under load against softening at high furnace temperatures, composed of a pressed, dried and uniformly preburnt mixture of 20 to 90 parts of chromium ore containing at least 30% of chro- 75 ao'raooc mium oxide, with 80 to 10 parts of magnesium oxide containing material which has been highly sintered at a temperature of at least 1600 C.

9. Improved refractory bricks which are stable under load against softening at high furnace temperatures, composed of a pressed, dried and uniformly preburnt mixture of 20 to 90 parts of chromiumorc containing at least 30% of chromium oxide, with 80 to parts of magnesium L0 oxide containing material, together with binding material, which has been highly sintered at a temperature of at least 1600 C.

10. The process formanufacturing highly -re 1 fractory bricks, which consists in mixing melted [5 magnesium oxide containing material with chroo sintered technical magnesia with chromium ore and shaping and burning the resulting mixture to form uniformly burned bricks.

' 12. The process for manufacturing highly re- 5 fractory bricks, which consists in mixing highly sintered magnesium oxide containing material, with chromium ore containing at least more than 30% of CrzOs, together with a metallic oxide compound and an organic binder, and forming, dry- 30 ing and uniformly burning the resulting mixture into bricks of the desired shape, preparatory to building the same into the structure of a furnace or the like.

13. The process for manufacturing highly refractory bricks, which consists in mixing highly sintered magnesium oxide containing material including some coarse granules, with chromium ore also including some coarse granules, a metallic oxide compound and an organic binder, shaping the resulting mixture and uniformly burning the shaped mixture to form prefired bricks preparatory to using the same in masonry and furnace structures.

-14. The process for manufacturing highly refractory bricks, which consists in mixing melted magnesium oxide containing material including some coarse particles, with chromium ore also including some coarse granules, a metallic oxide compound and an organic binder, shaping the resulting mixture'and uniformly burning the shaped mixture to form prefired bricks preparatory to using the same in masonry and furnace structures. I V

15. The process for manufacturing highly refractory bricks, which consists in mixing highly sintered magnesium oxide containing material with chromium ore, shaping the mixture under high pressure, drying the shaped and pressed mixture, and finally burning the same uniformly to form prefired bricks preparatory to using the same in masonry and furnace structures.

FRITZ HAR'I'MANN. 

